Mysteries of autoimmune diseases unravel

Just three months ago, Reagan Williams, 9, was dangerously sick with extremely high levels of sugar in her blood. Today she's back on her feet and enjoying her first days in fourth grade.

Last week, Kylynn Welsh, 18, was in critical condition on a ventilator in a New Jersey hospital, unable to breathe on her own because of swelling that closed her throat. On Sunday, she was released from the hospital and will soon be starting college.

These young people have very different illnesses with one thing in common: Their immune systems have gone awry.